Electronic components with plurality of contoured microelectronic spring contacts

ABSTRACT

An electronic component is disclosed, having a plurality of microelectronic spring contacts mounted to a planar face of the component. Each of the microelectronic spring contacts has a contoured beam, which may be formed of an integral layer of resilient material deposited over a contoured sacrificial substrate, and comprises a base mounted to the planar face of the component, a beam connected to the base at a first end of the beam, and a tip positioned at a free end of the beam opposite to the base. The beam has an unsupported span between its free end and its base. The microelectronic spring contacts are advantageously formed by depositing a resilient material over a molded, sacrificial substrate. The spring contacts may be provided with various innovative contoured shapes. In various embodiments of the invention, the electronic component comprises a semiconductor die, a semiconductor wafer, a LGA socket, an interposer, or a test head assembly.

RELATED APPLICATION

This application is a continuation-in-part of the co-pending U.S. patentapplication, filed Feb. 27, 2001, entitled “FORMING TOOL FOR FORMING ACONTOURED MICROELECTRONIC SPRING MOLD,” by Eldridge and Wenzel (Ser. No.09/795,772), which is a continuation-in-part of co-pending U.S. patentapplication, filed Feb. 12, 2001, entitled “METHOD FOR FORMINGMICROELECTRONIC SPRING STRUCTURES ON A SUBSTRATE,” by Eldridge andWenzel (Ser. No. 09/781,833), which is a continuation-in-part ofco-pending U.S. patent application Ser. No. 09/710,539, filed Nov. 9,2000, entitled “LITHOGRAPHIC SCALE MICROELECTRONIC SPRING STRUCTURESWITH IMPROVED CONTOURS,” by Eldridge and Wenzel, which applications areincorporated herein, in their entirety, by reference, and which arecollectively referred to herein as the “parent applications.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electronic component substrates withintegrated resilient spring contacts in the field of semiconductordevices, and more particularly to dice, wafers, Leadless Grid Array(“LGA”) sockets, and test head assemblies with resilient microelectronicspring contacts.

2. Description of Related Art

As semiconductor devices are made in increasingly smaller sizes, whileat the same time becoming increasingly complex, semiconductor die size,and the size of contacts pads on such dice, has also shrunk. This trendtowards ever-smaller and more powerful devices is projected to continue.The electronic components which use semiconductor devices are also beingmade in increasingly smaller sizes. New packaging technology, such asuse of Chip Scale Packages (“CSPs”) has evolved in response to thesetrends towards smaller packages, and more dense arrays of contacts.

The trend towards use of CSPs has led to new requirements in the fieldof semiconductor manufacturing and component assembly. Nearly allpresent and proposed CSPs use a solder ball as the first levelinterconnect element. In the field of testing, such CSPs require a waferor device-level contactor that can consistently and reliably makecontact with solder balls without requiring a costly or time-consumingcleaning step after each use. The contactor should also require a lowcontact force, deliver low electrical resistance and parasitics, andsurvive numerous testing cycles (such as several thousand compressioncycles at high temperature). The contactor should also scale easily,regardless of the number of dice per wafer, the number of terminals(contact pads or solder balls) per die, wafer diameter, terminal pitch,and electrical performance required. For example, current contactorsshould be capable of contacting as many as 100,000 terminals per wafer,at operating frequencies as high as one Gigahertz. Still higherdensities and operating frequencies are anticipated in the future. Ofcourse, the contactor must deliver all of this performance at aneconomically favorable cost.

Compact solder ball interconnect elements also place demandingrequirements on assembly of CSPs onto Printed Circuit Boards (“PCBs”).Silicon, as used in CSPs, has a rate of thermal expansion about fivetimes less than the material typically used in PCBs. A soldered jointbetween such mismatched materials is subject to stresses from thermalcycling, which over time can weaken the joint and degrade the electricalperformance of the soldered CSP/PCB system. Traditional approaches, suchas underfilling, can reduce problems caused by mismatched thermalproperties, but such approaches are difficult to scale down toincreasingly smaller sizes. In addition, the use of solder as a joiningmaterial creates a potential source of Alpha particles, which can reducethe reliability of adjacent semiconductor devices.

Microelectronic spring contacts made from relatively soft wire that isball-bonded to terminals of a semiconductor device or contactor, thenplated with a harder material for resiliency, have been usedsuccessfully with solder-ball type CSPs in the field of semiconductortesting. Exemplary spring contacts of this type, referred to herein as“composite contacts,” are disclosed, for example, in U.S. Pat. No.5,476,211 (Khandros), which is incorporated herein by reference.Composite contacts have proven to be reliable and scaleable as requiredfor modern semiconductor devices, and capable of repeatedly connectingto solder balls. Accordingly, composite contacts are well accepted inthe field of semiconductor testing, where they are used on probe cards,interposers, Leadless Grid Arrays (“LGA”) sockets, and other such testsubstrates. Use of composite contacts on a wafer-level tester, includingdirectly on a semiconductor wafer under test, is disclosed in U.S. Pat.No. 6,064,213 (Khandros et al.), which is incorporated herein, in itsentirety, by reference. Attaching the spring contacts to the wafer ordevice under test (as opposed to a test substrate) offers certainadvantages. These advantages include lower duty cycle requirements forthe contact, and primarily, the opportunity to use the spring contact asthe primary interconnection element during both testing and finalassembly, thereby eliminating the need for solder balls.

However, each composite contact must be individually attached at itsbase by a wire bond. The economics of individual wire-bonding can becomeunfavorable at volume mass-production levels, such as when individuallyattaching spring contacts to tens of thousands of terminals on a wafercontaining high-volume production semiconductor devices. Hence, use ofcomposite contacts has generally been limited to test substrates, suchas probe card assemblies and LGA production sockets, or to relativelylow-volume, high-performance devices. It has not yet been possible toprovide improved resilient contact elements with performance as good orbetter than composite contacts, but that can also be mass-produced at alower cost. It is desired, therefore, to provide wafer and semiconductordevices with such improved resilient contact elements. It is furtherdesired to provide electronic component substrates, such as probe cards,wafer contactors, LGA sockets, and test head assemblies, with thebenefits of such improved resilient contact elements.

SUMMARY OF THE INVENTION

Resilient microelectronic spring contact elements may be fabricated on asubstrate in a parallel process, for example, as disclosed in theco-owned U.S. Pat. No. 6,184,053 B1. This patent discloses a methodwherein a masking material may be applied to the surface of a substrateand patterned to have openings extending from areas on the substrate topositions which are above the surface of the substrate and which arealso laterally offset from the areas. A conductive metallic material isdeposited into the openings and is delimited thereby. A secondconductive material may then be deposited over the delimited areas ofthe conductive metallic material to a thickness sufficient to impartresiliency to a free standing contact element. The masking material maythen be removed to leave a free standing conductive and resilientcontact element attached to the substrate. This method may be refined ormodified in various ways, some of which are described in the '053patent.

Using this method or a similar method, pluralities of microelectronicspring contact elements may be made together on a substrate. Springcontacts which are made by patterning a masking layer and depositing aconductive and resilient layer on the masking layer, and/or in openingsof the masking layer, are referred to herein as “molded resilientcontacts.” In should be appreciated that other methods may be used tomake microelectronic spring contact elements in parallel, mass producedprocesses, and integrally formed contacts made by such other processesmay be suitable for use with the structures of the present invention. Ingeneral, “integrally formed” means deposited as a single, integral layerof material, and not assembled from discrete components that are affixedtogether. Methods for making integrally formed contacts need notnecessarily require the use of a sacrificial masking layer, such as isused to make molded resilient contacts.

A particularly useful advancement in molded resilient contact isdescribed in the co-pending parent applications referenced above. Usingspecial shaping techniques, the masking layer and/or a moldablesubstrate is contoured in a direction perpendicular to the substrate, toprovide a contoured mold. The resulting spring contacts, herein referredto as “contoured microelectronic spring contacts” or “contoured springcontacts,” are a type of integrally formed contact. Integrally formedcontacts, such as molded resilient contacts and contoured springcontacts, can provide performance comparable to composite contacts, withscalability to shrinking sizes and increasingly fine pitches equivalentor better than composite contacts, at potentially minimal manufacturingcost. The present invention exploits the advantages of integrally formedcontacts, such as contoured spring contacts, by applying them toelectronic components, such as semiconductor and test substrates ofvarious kinds.

In an embodiment of the invention, a semiconductor wafer is providedwith a plurality of integrally formed contacts, which are preferablycontoured spring contacts. Each contact is preferably connected to oneof the terminals on the wafer, either by directly mounting to aterminal, or through a redistribution trace. At least one stop structureis optionally provided adjacent to the spring contacts, to provide amounting surface for a mating component and/or to preventover-compression of the spring contacts. Typically, the spring contactsare configured with their contact tips aligned in substantially the sameplane. However, contact tips may be disposed in different planes formounting to a non-planar component, if required. The spring contacts maybe all of an identical type or shape; or in the alternative, springcontacts of different types or shapes may be provided on the same wafer.In a related embodiment of the invention, an individual semiconductordie is provided with contoured spring contacts, either by being dicedfrom a wafer as described above, or processed individually in likemanner.

Semiconductor devices with contacts according to the present inventionmay be either socketed to a mating electronic component, or soldered.Underfill is not required and typically is not preferred. Instead, anunfilled gap between the device and the mating component allows forrelative movement between the device and the mated component toaccommodate differences in thermal expansion and contraction, and allowsfor venting of any trapped moisture or other unwanted volatilematerials. An unfilled gap may also be advantageous for cooling thedevice, by providing an additional channel for forced convectivecooling. A stop structure, if present between the device and the matedcomponent, is preferably detached from at least one of the device or themated component, and therefore permits relative movement to accommodatethermal expansion and contraction. When devices provided with contactsaccording to the invention are soldered to a mated component, solderneed only be present on the distal end of each spring contact, therebydistancing it from the semiconductor device and greatly reducing thesoft error rate caused by solder-generated Alpha particles.

In an alternative embodiment, an LGA socket is provided with moldedresilient contacts, preferably contoured spring contacts. An LGA socketaccording to the present invention may be used in production and testenvironments, similarly to LGA sockets provided with composite springcontacts. In addition, because of the lower cost potential of contouredspring contacts, LGA sockets according to the present invention may beadapted for more widespread use as sockets in final assemblies. Forexample, an LGA socket according to the present invention may be usedfor connecting a microprocessor device to a printed circuit board.

In other embodiments of the invention, components of test headassemblies are provided with molded resilient contacts, contoured springcontacts and/or other microelectronic spring contacts. Components onwhich contoured spring contacts may be used according to the presentinvention include interposers, contactors, space transformers, andassemblies thereof. Similar components and assemblies provided withcomposite spring contacts are disclosed, for example, in U.S. Pat. No.6,064,213, referenced above. The present invention provides comparableperformance advantages at a potentially lower cost, using innovativecontact structures and other components in new arrangements.

A more complete understanding of the electronic components withpluralities of contoured microelectronic spring contacts will beafforded to those skilled in the art, as well as a realization ofadditional advantages and objects thereof, by a consideration of thefollowing detailed description of the preferred embodiment. Referencewill be made to the appended sheets of drawings which will first bedescribed briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a semiconductor wafer having aplurality of dice, and a plurality of microelectronic spring contactsmounted to the face of the wafer.

FIG. 1B is a detail view of the wafer shown in FIG. 1A, showing an arrayof microelectronic spring contacts on a die of the wafer.

FIG. 1C is a detail view of the array shown in FIG. 1B, showing acontoured microelectronic spring and surrounding stop structure.

FIG. 2A is a perspective view of an exemplary contoured microelectronicspring contact according to the present invention, having a V-shapedcross-section.

FIG. 2B is a cross-sectional view of the spring contact shown in FIG.2A, taken along the line indicated by arrows 2B in FIG. 2A, additionallyshowing a stop structure disposed over the base of the spring contact.

FIG. 2C shows a cross-sectional view, taken along the line indicated byarrows 2C in FIG. 2A, of an exemplary V-shaped section of a springcontact according to the present invention.

FIG. 2D shows a cross-section of an exemplary U-shaped section of aspring contact according to the present invention, viewed similarly toFIG. 2C.

FIG. 2E shows a cross-section of an exemplary spring contact with a flatrectangular cross-section, viewed similarly to FIG. 2C.

FIG. 2F shows a cross-section of an exemplary ribbed spring contactaccording to the present invention, viewed similarly to FIG. 2C.

FIG. 3 is a perspective view of an exemplary contoured microelectronicspring contact according to the present invention, having a U-shapedcross-section.

FIG. 4A is a perspective view of an exemplary contoured microelectronicspring contact according to the present invention, having a longitudinalrib extending along the beam of the spring contact.

FIG. 4B is a cross-sectional view of the spring contact shown in FIG.4A, taken along the line indicated by arrows 4B.

FIG. 5 is a perspective view of another exemplary contouredmicroelectronic spring contact according to the present invention,having a longitudinal rib extending along the beam of the springcontact.

FIG. 6A is a perspective view of an exemplary contoured microelectronicspring contact according to the present invention, having longitudinalcorrugations.

FIG. 6B is a cross-sectional view of the spring contact shown in FIG.6A, taken along the line indicated by arrows 6B.

FIG. 7 is a perspective view of an exemplary two of many microelectronicspring contacts with integral redistribution traces for use withelectronic components according to the invention.

FIG. 8 is a perspective view of an exemplary microelectronic spring withan integral redistribution trace having raised arches.

FIGS. 9A-9H are side cross-sectional views of a process structure andmaterials layered thereon during exemplary sequential steps of a processfor making a contoured microelectronic spring contact according to thepresent invention.

FIG. 10A is a perspective view of an exemplary chip-level forming toolaccording to the invention.

FIG. 10B is a detail perspective view of a portion of the forming toolshown in FIG. 10A, showing an embodiment with protruding embossingsurfaces.

FIG. 10C is a plan view of an exemplary wafer-level forming tool.

FIG. 10D is a detail perspective view of a typical impression made bythe tool shown in FIG. 10B in a moldable substrate.

FIG. 11A is a perspective exploded assembly view of an integratedcircuit (LGA) socket with contoured microelectronic spring contactsaccording to the invention.

FIG. 11B is a cross-sectional view showing a detail of the integratedcircuit socket shown in FIG. 11A.

FIG. 12A is a cross-sectional view showing a portion of an interposerwith contoured microelectronic spring contacts.

FIG. 12B is a cross-sectional view of an exemplary alternativeembodiment of a microelectronic spring suitable for use on an interposeror other electronic component.

FIG. 13 is a perspective view of an exemplary microelectronic springhaving a serpentine plan shape that is contoured to position the tipadjacent to the base.

FIGS. 14A-B are plan and elevation views, respectively, of exemplarypairs of microelectronic spring contacts for use on an electroniccomponent such as an interposer or contactor.

FIGS. 15A-B are plan and elevation views, respectively, of exemplaryalternative pairs of microelectronic spring contacts for use on anelectronic component such as an interposer or contactor.

FIGS. 16A-B are plan and elevation views, respectively, of an exemplarymicroelectronic spring having a pad-like tip.

FIG. 17 is a cross-sectional exploded assembly view of a test headassembly including an interposer and a contactor.

FIG. 18 is a cross-sectional exploded assembly view of a test headassembly with a contactor but no interposer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention satisfies the need for an electronic componentwith a plurality of microelectronic spring contacts, that overcomes thelimitations of prior art components provided with interconnectionelements. In the detailed description that follows, like elementnumerals are used to describe like elements illustrated in one or morefigures.

Contoured spring contacts according to the present invention areparticularly well-suited to making electrical connections tomicroelectronic devices having contact pads disposed at a fine-pitch, orwhere a large array of economical microelectronic spring contacts isdesired. “Fine-pitch” refers to microelectronic devices that have theircontact pads disposed at a spacing of less than about 130 microns (5mils), such as 65 microns (2.5 mils). However, structures of the presentinvention may also be used in coarser-pitch applications, if desired.The advantages of the present invention are realized in part from theclose tolerances and small sizes that can be realized by usinglithographic rather than mechanical techniques to fabricate the contactelements. However, the use of lithographic techniques does not, byitself, result in effective and reliable contact structures disposed ata fine-pitch. Contoured, microelectronic spring contacts according tothe structures and forms disclosed herein provide a greatly increasedprobability of success, and a greatly extended range of applications,compared to microelectronic spring contacts having essentially linearbeams with rectangular cross-sections.

Resilient contact structures, as known in the art, are subject toparticular performance requirements, which vary in degree betweenapplications. These requirements typically relate to contact force,wipe, clearance, contact angle, elastic range, z-extension,repeatability, electrical resistance, inductance, Hertzian stress at thecontact tip, and longevity. The contact structures according to thepresent invention provide advantages for each of the foregoingperformance areas, as is made apparent by the description that follows.

Semiconductor-Mounted Microelectronic Spring Contacts

Molded resilient contacts, and preferably, the contoured microelectronicspring contacts according to the present invention, are particularlysuitable for mounting directly to semiconductor components, such aswafers and dice, where the spring contacts may function as the primaryinterconnection element for the integrated circuit devices on the waferor die both during testing and during final assembly. The springcontacts may readily be fabricated in parallel, mass-productionprocesses that add relatively little to the cost of a wafer, die, orother device, and are readily scaleable to increasingly finer pitchesand higher contact densities. FIG. 1A shows an exemplary semiconductorwafer 100, such as a 200 mm wafer, comprising a plurality ofunsingulated dice 130, each of which is provided with a plurality ofcontoured spring contacts and at least one stop structure. Because ofthe typically small scale of the spring contacts, the spring contactsare not visible in this wafer-level view.

FIG. 1B shows an enlarged view of an individual die 130, on which anarray 140 of contoured spring contacts and a stop structure 116 arevisible. A pattern of streets 120 separates each die 130 from itsneighbors. Because of the small scale of the contoured spring contacts,structural details of the spring contacts are not visible in thisdie-level view. The exemplary array 140 comprises aligned rows of springcontacts and is relatively low-density, but it should be understood thatthe spring contacts may be provided on die 130 in any desired pattern orarrangement, and at much higher densities, finer pitches, and smallersizes than shown in FIG. 1B. Conversely, somewhat larger sizes ofcontacts may also be provided, if required. A pattern of redistributiontraces is optionally provided (in this view, such traces would be hiddenby the stop structure 116) to connect each spring contact to a terminalof the semiconductor device.

FIG. 1C shows an enlarged view of a single contoured spring contact 101mounted to an upper surface of die 130. Spring contact 101 comprises abeam 110, which is preferably a contoured, essentially sheet-like beam(as shown), a contact tip 106 positioned adjacent to a free end of thebeam, and a base 108 connected to a terminal of die 130, all of whichare integrally formed of a resilient, conductive material (generally,one or more layers of metal). Beam 110 extends from a side of base 108away from the upper surface of die 130 and beyond the distal (in thisview, upper) surface of stop structure 116, preferable to a distanceslightly less than the elastic range of the spring contact. Beam 110preferably has a contoured, sheet-like shape as a consequence of beingformed using a molding or equivalent process, as described herein. Stopstructure 116 preferably comprises a non-conductive material, forexample, a photo-resist such as SU-8, and may be configured as anintegrated sheet that surrounds all of the spring contacts (as shown),or as discrete, substantially non-resilient protrusions of materialhaving substantially co-planar surfaces distal from the surface of die130. The contoured spring contacts 106 of the present invention may beprovided in a wide variety of different shapes and configurations,without departing from the scope of the invention. Various exemplaryshapes and configurations, and further details regarding contouredspring contacts, are provided in the detailed description that follows,and in the incorporated references.

Contoured Microelectronic Spring Contracts

An exemplary microelectronic spring contact for use on dice, wafers, andother substrates is shown in FIGS. 2A and 2B. The cross-section shown inFIG. 2B is taken along the line indicated by arrows 2B in FIG. 2A. Asindicated by coordinate axes 211 and as used herein, the directionnormal to substrate 230 is the z-axis direction; the direction parallelto the projected length of beam 210 onto substrate 230 is the x-axisdirection; and the y-axis direction is normal to the plane defined bythe z-axis and x-axis.

The microelectronic spring contact 200 of FIGS. 2A and 2B comprises abase 208 and a beam 210 integrally formed from at least one layer ofelectrically conductive, resilient material. Substrate 230 is typicallya semiconductor substrate for an integrated circuit having numerouselectrical terminals, one of which is shown as the contact pad 214 inFIG. 2A. Contact pads, such as contact pad 214, are typically coupled byconductive traces, such as trace 218, to internal circuitry within theintegrated circuit. As known in the semiconductor art, substrate 230 istypically comprised of numerous layers, such as insulating layersinterposed with conducting and semiconducting layers, and a passivatinglayer optionally provided on the top surface 232 of the substrate 230.The passivating layer may be an insulating layer, a polysilicon layer,or other layers as known in the art. In some embodiments of theinvention, a contact pad 214 is electrically and mechanically coupled toan intermediate conducting layer 212 which is disposed above it, asshown in FIG. 2B. When present, intermediate layer 212 is typically amanufacturing artifact of a shorting layer used during an electroplatingstep of a process for forming the microelectronic spring contact. A stopstructure 216, as further described in the co-pending application Ser.No. 09/364855, filed Jul. 30, 1999, entitled “INTERCONNECT ASSEMBLIESAND METHODS,” by Eldridge and Mathieu, which is hereby incorporatedherein by reference, is optionally provided to prevent over-compressionof spring contact 200. Spring contact 200 provides for conduction ofelectrical signals and/or power between a tip 206 of beam 210, throughthe beam 210 of resilient material, intermediate layer 212, and contactpad 214, and finally through conductive trace 218 to an integratedcircuit in substrate 230. It should be appreciated that themicroelectronic spring contact 200 of FIGS. 2A and 2B may also be usedfor other types of interconnect assemblies, such as probe cardassemblies, interposers, and other connection systems where electricalcontact to or through a electronic component substrate is desired.

Microelectronic contact structures according to the present inventionare typically configured as a cantilevered beam, having a fixed base anda free end (tip), as described above. The beam is preferably blendedsmoothly at its ends to the base and the free tip. This basic geometryis preferred for contoured, microelectronic spring contact structuresaccording to the invention for several reasons. Integrated circuitmanufacturing processes, unlike alternative spring manufacturingprocesses such as wire forming, are best suited for making shapes thatmay be defined by projection onto a surface, such as by pattern masking.Such shapes are capable of being formed in a single step of amanufacturing process. In contrast, certain three dimensional curvescommonly found in wire-formed spring contacts, cross over themselves andcannot be defined by projection onto a surface. Such shapes thereforerequire multiple manufacturing steps to assemble, and cannot be made asa single, integrally formed piece using conventional integrated circuitmanufacturing processes. Therefore, the cantilevered beam configurationis desirable for lithographic spring contacts because fewer processsteps are required, and the spring contact can be formed from anintegrated mass of material. Additionally, the cantilevered beam iscapable of resilient motion in at least two dimensions, therebyproviding both wipe (desirable for making an electrical connection) andz-deflection, for compensating for misalignment between substrates, andfor providing the spring force needed for maintaining an electricalconnection.

Beam 210 is preferably tapered from a relatively wide width at its fixedbase to a relatively narrow width at its tip, to compensate for stressdistribution in the cantilevered beam. Such triangular-shaped beams arerelatively more structurally “efficient” (providing a higher contactforce for a beam of given mass) than rectangular shaped beams of thesame cross-sectional shape. However, a triangular shape may be lesselectrically efficient, because its current-carrying capacity isconstrained by the relatively small beam cross-section near the tip of atriangular beam. Thus, for certain applications, beams of constantcross-section may be preferred. Spring beams according to the presentinvention may thus be tapered, and/or be provided with constantcross-sectional areas, depending on the requirements of the application.

In addition, spring beams according to the present invention arepreferably contoured across their width and along their length.Contouring along the length of the beam may provide a more favorabledeflected shape of the beam for purposes of making an electricalconnection between two substrates. Contouring across the width of thebeam provides cross-sectional shapes having higher area moments ofinertia, compared to beams of the same mass having solid rectangularcross-sections. As is well understood in the structural arts, thestiffness of a beam of a given mass per unit length can be dramaticallyimproved by altering its cross-sectional shape. For example, a box beamis much stiffer than a solid rectangular rod having the same mass perunit length. Heretofore, it has not been feasible to provide contouredmicroelectronic contact structures with beams having higher area momentsof inertia than provided by solid rectangular cross-sections, at thesmall scale afforded by the present invention. Also, there has beenlittle or no motivation to reduce beam masses, because the cost of beammaterial for microelectronic spring contacts at small scales is notsignificant. However, according to the present invention, it is highlydesirable to reduce the mass of beam material in order to reduce thefabrication time required and the area occupied in a top down view ofthe structure, which determines the packing ability or minimum pitch atwhich the spring contacts may be mounted to a surface.

The theories and mathematical tools for predicting the structuralproperties of a contoured spring contact are well known in the art.Computational tools, such as finite element methods, further make itpossible to refine and optimize the shape of complex spring contacts inview of a variety of different loading conditions. Thus, using thecontoured shapes according to the present invention, it is now possibleto construct microelectronic spring contacts that have a much widerrange of performance properties than heretofore possible, while usingprocesses adapted from conventional manufacturing of integratedcircuits. In particular, the area moment of inertia, and thus the springrate, can be greatly increased by contouring the beam across its width.Additionally, the spring shape can also be optimized to reduce stressconcentration, resulting in more efficient use of material.Width-contoured spring contacts can thus be made with much less materialthan required for flat cross-section microelectronic spring contacts ofa comparable spring rate and strength.

Reducing the amount of material in a spring contact permits increasedprocessing throughput by decreasing the time required for depositing thematerial. In addition, thin-layer deposition techniques that werepreviously considered too slow or costly for thick layers may be viable.For example, a flat spring design might require a material thickness of25 microns (about 1 mil) to achieve a desired spring rate. Material ofthis thickness is typically deposited by electroplating, which is knownfor high throughput and cost-effectiveness in layers of this thickness.In contrast, a spring contoured according to the present invention canachieve the same spring rate using less material, for example, with only5 microns (0.2 mils) of material thickness. If electroplating is used,the processing throughput would be about 5 times higher for thecontoured spring contact. Additionally, CVD (chemical vapor deposition)and PVD (physical vapor deposition), typically limited to depositinglayers up to about 5 microns thick, become viable alternative depositionmethods for the spring metal.

Referring again to FIGS. 2A and 2B, contouring of spring beam 210 isvisible in both views. Beam 210 is preferably contoured across itswidth, for example, as shown in FIG. 2A illustrating a V-shaped beam. Anexemplary V-shaped cross-section of the beam, having a constantthickness “t,” is shown in more detail in FIG. 2C. It will be understoodthat an approximately constant thickness is a typical result ofdeposition processes such as electroplating, electroless plating, CVD,and PVD. From a comparison of the V-shape 240 shown in FIG. 2C to theflat rectangular cross-section 242 of equivalent thickness shown in FIG.2E, it is evident that the V-shaped cross-section has a substantiallygreater area moment of inertia, because the extension “a” of the shapeacross the neutral axis 215 is much greater. Thus, a V-shapedcross-section or other contour may be provided wherever the beam 210 isdesired to be stiffened. In the case of beam 210 shown in FIG. 2A, theV-shape is provided along the entire length of beam. If desired,however, the contoured cross-sectional shape may be provided along onlya portion of the beam length, or may be altered to provide varying beamstiffness along the length of beam. This may be desirable where aportion of the beam, for example, a tip portion, is designed to berelatively flexible compared to a different portion, for example, aportion near the base of the spring contact.

The present invention provides for spring contacts with specificproperties, such as specific spring rates, by contouring the beam shape.FIGS. 3-6B show exemplary alternative shapes for contoured beamsaccording to the invention. An exemplary U-shaped beam 300 on asubstrate 330 is shown in FIG. 3. U-shaped beam 300 has a cross-section244 as shown in FIG. 2D. Similarly to the V-shaped cross-section shownin FIG. 2C, the U-shaped cross-section 244 has a substantially higherarea moment of inertia relative to a beam with a flat rectangularcross-section. The U-shaped cross-section avoids the notch in the baseof the V-shape, which may cause undesirable stress concentration.However, the choice of a U-shaped cross-section relative to othersectional shapes may depend on considerations other than spring rate orother spring performance parameters. For example, manufacturability isan important consideration. Depending on the preferred manufacturingmethod, a particular shape, such as the U-shape, may be less costly tomanufacture than other shapes.

FIGS. 4A and 5 show various ribbed beams. FIG. 4A shows a ribbed springcontact 400 with a beam 410 having a rib 402 disposed above the surfaceof the beam. In structure 400, rib 402 runs the entire length of thebeam and base 408. As shown in FIG. 4B, spring contact 400 is alsopreferably contoured lengthwise along a compound curve 420, as describedin more detail in the parent application, Ser. No. 09/710,539 referencedabove. Rib 402 preferably follows the contour of curve 420, although itmay optionally be tapered in the z-direction to approach the uppersurface of beam 410 at its tip, as shown. FIG. 5 shows spring contact500 having a contoured beam 510 with a rib 502 disposed beneath thebeam. Rib 502 is terminated at an edge of base 508. Ribbed beams may besomewhat more costly to fabricate than V-shaped or U-shaped beams,because their more intricate shapes may require more intricate toolingand greater care during forming operations, but can provide certainadvantages. One advantage is that ribs can be placed across the width ofa beam wherever greater stiffness is desired. For example, as shown inFIG. 2F, ribs may be placed towards the edges of a beam to stiffen thebeam against torsion. This may be desirable where a beam is offset froma straight line, such as a serpentine or “C-shaped” beam as furtherdescribed below and in the parent application Ser. No. 09/710,539.Offset beams are subject to torsion in portions of the beam, andproperly placed ribs can stiffen an offset beam against torsion, wheredesired. Another advantage is that a rib can be extended into the baseof a microelectronic spring contact, as shown in FIGS. 4A and 4B. Thisprevents stress concentration and beam failure at the juncture 422between base 408 and beam 410, that can result from abrupt changes incross-sectional shape along a beam. Ribs 402 according to the presentinvention are preferably comprised of a folded portion of the beam 410,as shown in each of the foregoing FIGS. 2F and 4A-5. The folded portionis preferably configured so that no portion of the rib overlaps thebeam, when viewed from above the beam looking towards the substrate.Non-overlapping, folded ribs are readily formed by deposition of a layerof material over a molded form. A folded rib generally has the samethickness “t” as the beam, such as beams 410 and 510, and forms anintegral portion of the beam. The cross-section of ribs may berectangular, triangular, cylindrical, or almost any other desirednon-overlapping shape, and may taper in width or height along the lengthof the spring beam.

Contouring according to the present invention can be used for acompletely different purpose, apart from providing an increased areamoment of inertia for stiffening the spring contact, as described above.A spring contact may also be lengthwise contoured to decrease its“footprint,” i.e., the amount of projected area the spring occupies on asubstrate. FIG. 6A shows a corrugated spring contact 600 that iscontoured to decrease its footprint. An exemplary shape of thecorrugations is shown in edge view in FIG. 6B. It should be apparentthat the corrugations, like ribs, are readily formed by depositing alayer of resilient material over a contoured sacrificial layer,according to the method described below. It should be further apparentthat the ratio of the length “L” of the beam 610 to its projected length“L_(p)” on substrate 630 is increased by the corrugations. For acantilevered beam spring contacts having the same ratio of thickness tolength (i.e., “the same “t/L”), the elastic range is directlyproportional to the spring length “L.” Accordingly, the corrugations canprovide a greater elastic range “c” and a higher elastic deflectionratio (“c/h”) than an uncorrugated beam of equivalent projected lengthand z-extension, so long as the beam thickness of the spring contact isincreased in proportion to the increase in spring length.

A further advantage of a corrugated spring contact is that the bendingmoment experienced by the spring base for a given force applied at thespring tip is reduced proportionally to the reduction of projectedlength “L_(p).” Reducing the bending moment at the base reduces thespring base area required to achieve adequate adhesion of the springcontact to the substrate. A reduced base area, in turn, further reducesthe footprint of the spring contact. Additionally, corrugations provideresiliency in the horizontal plane, parallel to the substrate (i.e., inthe “x-y plane”). That is, corrugated spring contacts can be made moremechanically compliant in the x-y plane than straight and convexdesigns. This is advantageous where the spring tip will be fixed inplace (e.g., if the spring tip will be soldered to a mating contactpad). The resiliency in the x-y plane compensates for thermal expansiondifferentials, misalignment, vibration and other stresses betweenconnected components, thereby increasing the reliability of theconnection.

Microelectronic spring contacts may be provided with integralredistribution traces, thereby reducing the cost of providing spacetransformation (either from a compact arrangement to a less compactarrangement, or vice-versa) to an array of terminals. FIG. 7 shows anexemplary plurality (two of many shown) of contoured microelectronicspring contacts 700, each with an integral redistribution trace 720.Each trace 720 is preferably formed simultaneously with the base 708 andcantilever beam of structures 700, such as by using a patterneddeposition technique as previously described herein, or in theincorporated references. Pitch spreading, such as from a pitch “P1” atterminals 722, to a larger pitch “P2” at contact tips 706, may thusreadily be achieved in a single process step. Integral redistributiontraces have not been contemplated and are not feasible for prior artmicroelectronic spring contacts. However, the process according to thepresent invention is suitable for use with integral traces because thebase 708 of the spring contact may be formed on the underlying substratein much the same way as a redistribution trace. Greater stiffness andstrength may be provided to the beam of structure 700 by a subsequentdeposition step, for example, by plating the base and beam of structure700 with an additional layer of resilient material, while optionallymasking the integral redistribution trace 720.

Other structures may additionally be integrally formed with a springcontact according to the present invention. FIG. 8 shows a springcontact 800 having one or more raised bumps or arches 816 integraltherewith. Raised arches 816 are shown in the relatively narrow integralredistribution trace 820, but it should be apparent that similar raisedfeatures may be provided in the base 808, or in a separate location onsubstrate 830. Raised features or arches 816 may function as stopstructures for spring contact 800, thereby reducing or eliminating theneed to form a stop structure in a separate step. When provided in aredistribution trace, as shown in FIG. 8, an arch may provide theadditional or alternative function of stress relief for the trace 820and/or between the spring contact 800 and trace 820. A further possibleconfiguration and function for a raised feature is as a protruding,substantially non-resilient interconnection element. It should beapparent that various types of raised features may be provided using thesame process steps as used to mold the contoured spring contact 800,e.g., by forming a protrusion of moldable substrate and then depositinga resilient material on the protrusion. The moldable substrate under theprotrusion may be removed in a subsequent process step (as it is under aspring contact), or left in place, depending on the desired function ofthe raised feature. Raised features may be semi-cylindrical in shape, asshown, or in other open tubular shapes such as square, rectangular, ortriangular. Raised features may also comprise closed shapes such ashemispheres, cubes, inverted cones, pyramids, and the like, especiallyfor applications for which it is not necessary or desirable to removethe moldable substrate under the raised feature. Furthermore, asdiscussed above with respect to structure 700, resilient material may bedeposited to different depths on any selected ones of the raised arches816, redistribution trace 820, or spring contact 800 using a series ofpattern masking and depositing steps, as disclosed in the incorporatedreferences.

Method for Making Contoured Spring Contracts

Contoured spring contacts may be formed by depositing an integratedlayer of resilient material over a contoured sacrificial layer,sometimes referred to herein as “molding.” The layer of resilientmaterial is preferably built up on the sacrificial layer as a conformalcoating deposited by a method such as electroplating. An embodiment ofthis molding technique for making contoured spring contacts according tothe present invention is illustrated in FIGS. 9A-9H. The fabrication ofa single contact structure will be described as exemplary of fabricatinga plurality of such contact structures, preferably all at the same timeon the same electronic component. For many applications, each of thecontact structures fabricated on a single component will besubstantially identical to one another. In the alternative, thedimensions and shape of each contact structure can individually becontrolled and determined by the designer for given applicationrequirements, and fabricated using the method described herein as willbe apparent to one skilled in the art.

The method described herein is provided as merely exemplary of aparticularly suitable way of making integrally formed spring contacts,and especially contoured spring contacts. The example is not intended tolimit the invention. For example, the invention is not limited tostructures that make use of spring contacts that are formed using asacrificial layer. To the extent that similar spring contacts may beformed without using a sacrificial layer, such spring contacts may beadapted for use with the present invention.

Referring to FIG. 9A, in a preparatory step of a method for making acontoured spring contact, an electronic component substrate 930,optionally provided with contact pads 914 for connecting to anintegrated circuit, is coated with a moldable sacrificial layer 950.Sacrificial layer 950 may be any number of materials, such as PMMA (polymethyl methacrylate), which can be coated on a substrate to the desiredthickness, which will deform when pressed with a mold or stamp, whichwill receive the resilient material to be deposited thereon, and whichcan then readily be removed without damaging the spring contacts 900.Additional candidate materials for layer 950 include acrylic polymers,polycarbonate, polyurethane, ABS plastic, various photo-resist resinssuch as Novolac resins, epoxies and waxes. The sacrificial layer 950preferably has a uniform thickness sufficient to provide a mold formslightly deeper than the desired z-extension “h” of the finished springcontacts. For example, if the desired z-extension is 50 microns (about 2mils), layer 950 may have a thickness, after being impressed with tool960, of 55 microns (2.2 mils). Various methods known in the art, forexample, spin coating and lamination, may be used to deposit layer 950onto substrate 930.

Also, a forming tool 960, having a molding face provided with differentmolding regions 964, 966, and 968, is prepared for molding sacrificiallayer 950. Various methods may be used to prepare tool 960, as describedin more detail below and in the incorporated references. Maximallyprotruding molding areas 964 of tool 960 are used for deforming thesacrificial layer 950 in the area of the contact pads 914, where thebases 908 of contact structures 900 will be formed. Contoured moldingregions 966 are used for deforming layer 950 where the contoured beams910 of contact structures 900 will be formed. In FIG. 9A, a contouredregion for making a V-shaped beam is shown in lengthwise cross-section.An embossing tooth 962 may be provided with at least one maximallyprotruding region 964 and at least one contoured region 966. Maximallyrecessed molding regions 968 are used for receiving excess material,i.e., “flash,” pushed aside by teeth 962. Molding regions 968 may beused to define spacing between adjacent spring contacts 900 on substrate930. Alternatively, or in addition, spacing may be determined by asubsequent patterning step. Depending on the choice of materials forsacrificial layer 950 and forming tool 960, a layer of mold releasematerial (not shown) is optionally provided on the molding face of tool960. It should be recognized that further layers and material may bepresent on substrate 930 without departing from the method describedherein. For example, a metallic shorting layer (not shown) is optionallyprovided between layer 950 and substrate 930, to protect any integratedcircuits embedded in the substrate during processing operations.

In a molding step illustrated in FIG. 9B, the forming tool 960 isapplied against substrate 930 with sufficient pressure to bring themaximally protruding areas 964 of teeth 962 nearly to the surface ofsubstrate 930, and to fully mold layer 950 in all contoured moldingregions 966. To avoid damaging substrate 930, teeth 962 are preferablynot brought into contact with substrate 930. In a preferred embodiment,when teeth 962 have sunk into layer 950 to the desired depth, flashsubstantially fills the maximally recessed regions 968 to form a surfacesufficiently uniform to permit later deposition of a layer of maskingmaterial between the spring contacts after the forming tool 960 isremoved from layer 950. Forming tool 960 may be heated to assistdeformation of layer 950, and then cooled to harden layer 950 intoplace. In an alternative embodiment, layer 950 is selected of a materialthat is sufficiently deformable to flow under pressure withoutapplication of heat, and sufficiently viscous to hold its shape aftertool 960 is removed. In yet another alternative embodiment, heat, UVlight, or chemical catalysts are used to harden sacrificial layer 950while under forming tool 960, and then the tool is removed. Whatevermolding technique is used, the cycle times are preferably relativelyshort to permit faster manufacturing throughput.

FIG. 9C shows the shape of the sacrificial layer 950 after removal ofthe forming tool 960. A thin layer of residue 952 is present over thearea of each contact pad 914. Negative mold surfaces 954 are alsopresent, each bearing a negative impression or “plug” of the contouredbeams to be formed therein. It is necessary to remove the residue 952 inorder to expose the substrate 930 in the areas where the bases 908 ofthe contact structures 900 will be formed. To remove the residue 952,the entire substrate with its molded layer 950 may be isotropicallyetched by immersion in a bath of etchants, by oxygen plasma, or othermethod as known in the art. Isotropic etching is suitable for relativelyflat substrates for which the residue layer 952 is of a uniformthickness in all places where the spring bases 28 will be formed.Preferably, the isotropic etch is performed so as to remove the residue952 while at the same time reducing the thickness of layer 950 to equalthe desired z-extension of the finished spring contacts 900. In thealternative, an anisotropic etching method that etches more rapidly inthe z-direction, such as reactive ion etching, may be used. Az-anisotropic etch is preferably used in cases where the substrate isrelatively uneven, and the thickness of residue 952 is not uniformacross substrate 930.

The appearance of the molded sacrificial layer 950 after etching isshown in FIG. 9D. The contact pads 914 are preferably exposed, alongwith a surrounding exposed area 956 of substrate 930 sufficient forproviding adhesion of the base 908. In typical semiconductorapplications, an exposed area 956 of between about 10,000 and about40,000 square microns, most preferably in excess of about 30,000 squaremicrons, is provided. After etching, the mold surfaces 954 preferablytake on the desired contoured shape, and the distal tips of all moldsurfaces 954 on substrate 930 are preferably within essentially the sameplane.

FIG. 9E shows substrate 930 after application of a seed layer 966 and amasking layer 968. The seed layer is typically a relatively thin layer,such as about 4500 Å (Angstroms; or about 0.45 microns) thick, ofsputtered metal for electroplating the resilient spring material. In thealternative, surface modifications of layer 950, e.g. plasma treatment,may be used to render it conductive, thereby providing the conductivityneeded for electroplating. It should be appreciated that in FIGS. 9E-9H,the relative thickness of seed layer 966 is exaggerated. Masking layer968 may be selected from various commercially available photoresistmaterials, such as an electrodeposited resist, Novolac liquid resists,or a negative-acting dry film photo-resist. Masking layer 968 is curedin an appropriate manner, for example by exposing it to UV light througha pattern mask, except where the spring contacts are to be formed. Theuncured portions of masking layer 968 are then dissolved away by asuitable solvent, as known in the art.

After the uncured portions of the masking layer are dissolved away,exposed areas of seed layer are revealed, comprising mold forms 970 fora spring contact, as shown in FIG. 9F. Mold forms 970 may have theprojected shape of the desired microelectronic spring contact. Forexample, if a triangular beam is desired, the mold form may have agenerally triangular shape, in plan view. In the alternative, the moldform may have a generally elongated shape upon which one or more springcontacts may be patterned using a method such as pattern masking. Ineither case, after the mold form 970 is prepared, one or more layers ofresilient material may then be electroplated or otherwise deposited ontothe seed layer in the mold forms 970, using various methods as known inthe art. Where the seed layer is covered by resist layer 968, noelectroplating will occur. In the alternative, a layer of resilientmaterial may be built up using a process such as CVD or PVD selectivelyapplied to mold forms 970 through a mask, eliminating the need for seedlayer 966. Alternative line-of-sight deposition methods may make use ofa pattern mask, obviating the need for masking layer 968 also. Using anyof various deposition methods, a spring contact comprising an integrallyformed base 908 and beam 910 is deposited on the mold form 970, as shownin FIG. 9G. The cured resist layer 968, sacrificial material 950, andany residual seed layer 966, are then dissolved away using a suitableetchant that is relatively slow to etch the substrate 930 and theresilient spring material, as known in the art. Freestanding springcontacts 900 mounted to contact pads 914 on electronic componentsubstrate 930, as shown in FIG. 9H, are the result.

Suitable materials for the resilient spring material include but are notlimited to: nickel, and its alloys; copper, cobalt, iron, and theiralloys; gold (especially hard gold) and silver, both of which exhibitexcellent current-carrying capabilities and good contact resistivitycharacteristics; elements of the platinum group; noble metals;semi-noble metals and their alloys, particularly elements of thepalladium group and their alloys; and tungsten, molybdenum and otherrefractory metals and their alloys. Use of nickel and nickel alloys isparticularly preferred. In cases where a solder-like finish is desired,tin, lead, bismuth, indium, gallium and their alloys can also be used.The resilient material may further be comprised of more than one layer.For example, the resilient material may be comprised of two metallayers, wherein a first metal layer, such as nickel or an alloy thereof,is selected for its resiliency properties and a second metal layer, suchas gold, is selected for its electrical conductivity properties.Additionally, layers of conductive and insulating materials may bedeposited to form transmission line-like structures.

It should be recognized that numerous variations of the above-describedsequence of steps will become apparent to one skilled in the art, forproducing integrally formed spring contacts according to the presentinvention. For example, a spring contact structure may be fabricated atan area on a substrate which is remote from a contact pad to which it iselectrically connected. Generally, the spring contact structure may bemounted to a conductive line that extends from a contact pad of thesubstrate to a remote position. In this manner, a plurality of springcontact structures can be mounted to the substrate so that their tipsare disposed in a pattern and at positions which are not dependent onthe pattern of the contact pads on the substrate. Numerous otheralternative methods for forming contoured microelectronic springcontacts for use in the invention are disclosed in the parentapplication entitled “METHOD FOR FORMING MICROELECTRONIC SPRINGSTRUCTURES ON A SUBSTRATE,” referenced above.

Although various adaptations may be made to the method disclosed herein,in general, a molding or other forming process using a relatively thicklayer of sacrificial material, such as layer 950, is preferred forproviding adequate z-extension without requiring building up of multiplelayers of photo-resist. Additionally, use of a deformable sacrificialmaterial provides for duplication and mass production of relativelycomplex, contoured beam shapes. Accordingly, in the preferredembodiments, the entire contoured microelectronic spring contact (withthe exception of optional features such as separate tips) may be definedin a layer of material deposited (such as by electroplating, CVD, orPVD) on the surface of a mold form. The resulting spring contacts arethus comprised of an integral sheet, which may comprise a single layer,or multiple coextensive layers, of resilient, conductive, and/orresistive material. The integrated sheet may be folded and contoured,and is preferably essentially free of any overlapping portion in thedirection that the materials are deposited (typically from above thestructure towards a substrate), so it may be more readily formed bydepositing a layer or layers of material in a single open mold,according to the process described above. However, a substantial amountof overlap may be achieved using some deposition methods, such aselectroplating in conjunction with a “robber” to drive electricallycharged material under an overhang.

Forming Tool for Microelectronic Spring Molds

It should be appreciated that a tool (variously referred to as aforming, stamping, molding, or embossing tool) for forming a moldingsurface for a contoured microelectronic spring contact is an importantand novel aspect of the present invention. An exemplary chip-levelforming tool 100 is shown in FIG. 10A. Forming tool 1000 comprises abase 1002 comprised of a tool material. The tool material may be anymaterial which is sufficiently hard, strong, and formable on the desiredscale. A wide variety of materials are suitable; however, for use withthe methods disclosed herein, preferred materials include metals such asnickel, steel, or aluminum; relatively hard plastics such as polyamides,polyimides, and epoxies; formable nonmetallic inorganic materials suchas glass and fused silica; and selected photoresist materials such asSU-8. In an embodiment of the invention, the tool material is providedwith microscopic pores to remove gas that may become trapped between theforming tool and the molding substrate during a stamping operation. Suchpores may be provided by fabricating the forming tool out of a porousmaterial such as a Micropore™ glass filter or glass frit. Pores may alsobe individually machined (such as by laser ablation) at the locationswhere gases are most likely to become trapped. A smooth, gas-permeablemembrane such as Gore-Tex™ can also be applied over a porous surface toincrease lubricity and act as a release agent during molding operations.To reduce or eliminate the need for pores and gas permeability, theforming tool may be applied in a low vacuum environment.

Base 1002 comprises an embossing face 1004 on which a contouredembossing surface 1010, comprising at least one embossing tooth 1012, isdisposed. In an embodiment of the invention, a plurality of embossingteeth 1006 are disposed on embossing face 1004, as shown in FIG. 10A.Each embossing tooth 1012 of teeth 1006 is configured to form a mold fora freestanding resilient microelectronic spring when tool 1000 isimpressed into a layer of moldable material. In an embodiment of theinvention, each tooth 1012 of the plurality of teeth 1006 has asubstantially identical surface contour, corresponding to a moldingsurface for a microelectronic spring mold. The teeth 1006 may bearranged in a rectangular array, or in any pattern desired on face 1004.Teeth 1006 may be made substantially identical to each other, or maycomprise various different shapes on the same forming tool 1000,depending on the desired spring contacts to be formed.

Although embossing face 1004 is shown as being substantially planarunderneath teeth 1006, face 1004 may be provided with non-planarfeatures adjacent to teeth 1006, so long as any such non-planar featuresdo not interfere with the molding function of teeth 1006. For example,embossing face 1004 may be provided with recesses, streets, or throughholes (not shown) interspersed between individual ones of teeth 1006,for receiving excess mold material, i.e., flash, when tool 1000 isimpressed into a layer of such material. For further example, embossingsurface 1010 may be provided with protruding tooling stops or raisedseals (not shown) adjacent to a periphery of the embossing face 1004.Such auxiliary features, whether recessed or protruding, may be used toenhance the molding function of tool 1000, but do not alter theessential function of embossing face 1004 and embossing surface 1010thereon, which is to form a mold for one or more freestanding resilientmicroelectronic spring contacts. Base 1002 is optionally mounted to asupport substrate 1008 for assembly into a multi-faceted forming toolassembly, or for mounting to a stamping jig or stamping equipment.

Geometric details of forming tool 1000 are shown in FIG. 10B. Each tooth1012 comprises a protruding area 1014 and a sloped portion 1016 recedingfrom the protruding area 1014. Sloped portion 1016 is configured to forma beam portion of a mold for a freestanding microelectronic springcontact, and defines the contoured shape of the beam. In someembodiments of the invention, sloped portion comprises a contour in alength direction, such as an S-curve, a convex curve, a concave curve,or a sinusoid. For example, FIG. 10B shows each tooth 1012 with a slopedportion 1016 comprising a convex contour. Protruding area 1014 isconfigured to form a base portion of a mold for a freestandingmicroelectronic spring contact, which is the area where the base of thespring contact is to be formed. A step 1020 is optionally provided tovertically offset the sloped portion 1016 from area 1014. Alternatively,sloped portion 1016 is blended smoothly into area 1014, depending on thedesired spring shape.

In a typical embodiment of the invention, each protruding area 1014 issubstantially planar, comprises a maximally protruding portion of eachtooth 1012, and is aligned in the same plane as adjacent protrudingareas 1014 of adjacent teeth 1006, as shown in FIG. 10B. Thisconfiguration is preferred for forming base portions of molds onsubstantially planar substrates. Similarly, in a typical embodiment,each distal end 1018 of sloped portions 1016 is aligned in the sameplane as adjacent distal ends 1018, to form molding surfaces for springcontacts with co-planar tips. However, for providing spring molds fornon-planar substrates, protruding areas 1014, and distal ends 1018 maybe configured to not be co-planar with corresponding portions ofadjacent teeth 1006.

Various exemplary configurations for molding teeth, and other methodsfor making forming tools, are described in the parent applicationentitled “TOOL FOR FORMING MICROELECTRONIC SPRING STRUCTURES ON ASUBSTRATE” and referenced above. It should be appreciated that theinvention is not limited to the particular shapes disclosed therein, andencompasses any shape for forming a mold for a freestandingmicroelectronic spring having a sloped beam. In addition, the inventionencompasses forming tools having teeth with various different shapes, aswell as tools having only identical teeth on the embossing surface. Itshould further be appreciated that a forming tool may be configured tofunction as one of two or more forming tools for successive applicationto a molding substrate, without departing from the scope of theinvention.

Chip-level forming tools, such as shown in FIG. 10A, may be assembledinto larger tool assemblies, such as the wafer level forming tool shownin plan view in FIG. 10C. Each forming tool 1000, optionally mounted toa support substrate 1008, is arranged on an assembly substrate 1024 toform wafer-level tool 1022. Individual forming tools 1000 may bearranged in an array on substrate 1024 corresponding to pattern of diceon the wafer. In this configuration, a plurality of microelectronicspring molds may be formed in parallel (that is, during a singleprocess) on all dice, or a selected portion of dice, on a semiconductorwafer. It should be apparent that various configurations of individualforming tools 1000 may be assembled in various arrangements, withoutdeparting from the scope of the invention. For example, a single tool1000 may be configured to form spring molds on more than one die at atime. For further example, a wafer lever tool 1022 may be configured tocontact only a portion of dice on a wafer. Assembly of a larger formingtool, such as wafer-level tool 1022, from individual units, such aschip-level tool 1000, provides advantages associated with assemblies,such as greater versatility, ease of repair, and higher yield. However,a wafer-level forming tool may also be formed out of an integrated pieceof tool material, if desired.

FIG. 10D shows a partial perspective view of a layer of moldablematerial 1026 after being impressed with a forming tool such as the toolshown in FIG. 10A. A plurality of molds for microelectronic springcontacts, such as mold 1030, have been formed in a surface 1040 ofmoldable layer 1026. Each mold 1030 comprises a beam molding surface1032, for a beam of a microelectronic spring contact, and a base moldingsurface 1034, which preferably comprises an exposed surface of theunderlying, relatively hard and non-moldable substrate 1028.Alternatively, the base molding surface 1034 is adjacent to the surfaceof substrate 1028, and a portion of moldable layer 1026 is removed underbase molding surface 1034 in a subsequent step. Each mold 1030optionally includes a stepped portion 1036, corresponding to an optionalstep, such as step 1020 shown in FIG. 10B, on tooth 1012. The formingtool 1000 is comprised of a material harder than moldable layer 1026,and is preferably coated with, or comprised of, a material that will notadhere to layer 1026, so that the forming tool may be cleanly removedafter molding. Where molds 1030 are recessed into the mold material, asshown in FIG. 10B, each mold 1030 is provided with a lip 1042. Lip 1042may be flush with the side walls of recessed mold 1030 (as shown);alternatively, lip 1042 may overhang the side walls. Molds 1030 aresuitable for forming microelectronic spring contacts, as furtherdescribed in the co-pending parent applications referenced above, and inparticular, the application entitled “METHOD FOR FORMING MICROELECTRONICSPRING STRUCTURES ON A SUBSTRATE.”

LGA Socket Assemblies

Like composite spring contacts, the integrally formed contacts accordingto the present invention, such as contoured microelectronic springcontacts, are well suited for use in LGA production sockets, whileoffering the potential advantages of lower cost, finer pitch, highercontact density, and lower contact force. FIG. 11A shows an explodedview of an LGA socket assembly 1100 with contoured microelectronicspring contacts 1106. LGA socket assembly comprises a lid 1150, an LGApackage 1140, and an LGA alignment frame 1102 with microelectronicspring contacts 1106. LGA alignment frame 1102 is a type of integratedcircuit socket, comprised of a substrate 1130 having a mountingface-1132, and a plurality of contoured microelectronic spring contacts1106 mounted to face 1132 and oriented to make contact withcorresponding pads (hidden from view in FIG. 11A) of the LGA package1140. Any number of microelectronic spring contacts 1106 may be presenton face 1132. In typical applications, the number of spring contactswill be between about three hundred and about three thousand, althoughfewer or more contacts may also be provided. The spring contacts aretypically disposed on a pitch of between about 0.5 and 1.5 mm (about 20to 60 mil), although finer or coarser pitches may be accommodated, ifdesired. It should be appreciated, therefore, that for illustrativeclarity the spring contacts 1106 shown in FIG. 11A are not drawn to ascale that reflects typical sizes and contact densities for LGApackages. In most applications, the contact sizes would be smaller, andthe contact density higher, than that illustrated. A stop structure 1116is optionally provided on face 1132 between all (or between selectedones) of microelectronic spring contacts 1106.

LGA package assembly may be configured in various differentconfigurations. In the configuration shown, the mounting face 1132 issurrounded by a raised mounting frame 1104 which is integral withsubstrate 1130. Threaded holes 1154 are provided for fasteners 1152 (oneof many shown), which attach lid 1150 to the LGA alignment frame 1102.Mounting frame 104 may also be provided with through holes 1156 forhandling purposes. The raised mounting frame 1104 is configured to fitaround LGA package 1140, which is compressed against the spring contacts1106 (and against the stop structure 1116, if present) by lid 1150. Lid1150 is optionally provided with at least one compression spring, suchas a leaf spring, on its underside (not shown), to bear against LGApackage 1140, as known in the art. Various other LGA package assemblyconfigurations may be suitable. For example, a hinged lid provided witha compression spring to compress LGA package 1140 against springcontacts 1106 may be provided, in lieu of the separate lid 1150.

FIG. 11B shows a typical detail of a contoured microelectronic spring1106 on substrate 1130. Substrate 1130 is preferably comprised of aconventional packaging material, such as FR-4, ceramic, BT resin, orother available material. Substrate 1130 is prepared for mounting springcontacts 1106 by planarization of face 1132 as known in the art. Springcontact 1106 is preferably a contoured microelectronic spring contactaccording to the present invention, and may be configured in variousdifferent shapes, according to requirements of the application. Eachspring contact 1106 is mounted at its base to a pad or terminal 1114 onface 1132, which is connected by via 1128 to a corresponding pad orterminal 1124 on an opposite face 1136 of substrate 1130. The tip ofeach contact 1106 is positioned to contact a corresponding pad on LGApackage 1140. Each contact is optionally provided with a stop structure1116, which protects the spring contacts 1106 from over-compression, andthereby may simplify the mounting of an LGA package in the alignmentframe 1102. The LGA alignment frame may be connected to a system boardusing any conventional method, such as a solder ball or bump 1134between terminal 1124 and a corresponding terminal on the system board.In the alternative, a contoured microelectronic spring contact may beprovided on the lower terminal 1124, or on a corresponding terminal ofthe system board, for connecting to lower terminal 1124. Various otherconfigurations for LGA package assemblies using contouredmicroelectronic spring contacts according to the present invention willbe apparent to one skilled in the art.

Interposers, and Contracts for use Thereon

The contoured spring contacts of the present invention are also suitablefor use on interposer substrates in lieu of prior art interconnectionelements, such as the composite microelectronic spring contacts used oninterposers as disclosed, for example, in the above referenced U.S. Pat.No. 5,974,662. As known in the art, an interposer is a generally planar,relatively thin substrate having two opposite surfaces (such as an uppersurface and a lower surface) and a plurality of outwardly extendingresilient interconnection elements on both surfaces. Eachinterconnection element on one surface (e.g., an upper surface) isconnected to a corresponding interconnection element on the oppositesurface (e.g., a lower surface). Interposers are typically used tocompensate for non-planarity between two mating substrates, such asbetween a probe card and a device under test.

FIGS. 12A-B show details of an exemplary portion of an interposer 1200provided with contoured spring contacts 1240, 1250, and/or 1260according to the present invention. A design criteria of particularimportance for spring contacts used on interposers is the working rangeof the spring contact, which is the portion of the elastic range ofdeflection of the spring over which the contact force is within a usablerange. For example, if the contact force at the spring tip variesbetween 0 grams when the spring contact is undeflected to 10 grams atthe elastic limit of the spring contact, and the minimum contact forcerequired to make a reliable electrical contact is one gram while themaximum allowable contact force is nine grams, the working range of thespring contact will be approximately 80% of its elastic range, providedthat the contact force varies in an approximately linear fashion overthe elastic range. In an interposer, the working range of the springcontacts on each surface should be sufficient to compensate for—that is,greater than—non-planarity between the mating substrate or device forwhich the interposer is intended to compensate.

The working range of a spring contact which is provided with a stopstructure, such as stop structure 1216 shown in FIGS. 12A-B, willtypically be a fixed percentage (e.g., 80%) of the height of the springtip 1206 over the distal surface of the stop structure (sometimes calledz-extension), shown as the distances “z₁” and “z_(2,)” for the upper andlower surfaces of interposer 1200, respectively. The total working range“Z” of the interposer will then be a fixed percentage of the sum (z₁+z₂)of the z-extensions for spring contacts on the two opposing surfaces ofthe interposer. For many applications, the non-planarity of principleconcern will be non-parallelism between the mating substrates, which maybe expressed as an angular value, e.g., “α” A given interposer of span“L” and total working range Z will thus be capable of compensating fornon-parallelism α determined by tan⁻¹(Z/L). The span L of an interposeris generally fixed by the requirements of the test substrate. Therefore,the total working range Z of the contoured spring contacts, which is inturn related to the z-extension of the spring contacts, will be ofparticular importance to the compliance of the interposer.

For many interposer applications, it may be necessary to providecontoured microelectronic spring contacts that have a greater workingrange than spring contacts for other substrates, such as wafers, dice,and LGA sockets. It is usually not feasible (or if feasible, is notdesirable) to achieve an increased working range merely by increasingthe slope of a cantilevered beam portion of the spring contact, that is,by orienting the beam more perpendicularly to the substrate 1230. Aperpendicularly-oriented beam flexes more like a column than a leafspring, which typically results in a decrease in working range andundesirable stress concentration. Generally, a beam sloped more thanabout 60° from the substrate is not preferred, and a preferred beamslope may be substantially less, such as about 30°. Some increase inworking range may be realized by making a spring contact of a givenshape larger without increasing the beam slope, as exemplified bycomparison of larger spring contact 1260, shown in FIG. 12B, with thesmaller spring contact 1240 shown in FIG. 12A. Both spring contacts1240, 1260 have a similar cross-sectional shape, although spring contact1260 additionally includes a rib 1262 for increased strength andstiffness, because of its longer cantilevered beam length. Larger springcontact 1260 has a larger footprint than smaller spring contact 1240,which may be disadvantageous or not feasible for some applications. Amore compact design for increased working range is exemplified by springcontact 1250, shown on the upper surface of substrate 1230 in FIG. 12A.Spring contact 1250 is serpentine in plan, preferably having a tip 1206vertically offset from base 1208 a relatively small distance, so as tominimize the moment on base 1208 caused by contact forces imposed at tip1206, and hence to minimize the footprint required for the base. Aperspective view of a contoured spring contact 1300 having a serpentineplan form similar to contact 1250 is shown in FIG. 13. Contact 1300 hasa beam 1310 with a generally U-shaped plan shape, but it should beapparent that various other curved shapes would provide similaradvantages.

Various other exemplary configurations of contoured microelectronicspring contacts with curved or serpentine plan shapes are shown in FIGS.14A-B and 15A-B. Opposing pairs 1400 of curved contacts 1401 having arelatively steep slope are shown in FIGS. 14A-B mounted to contact pads1414 which are connected by via 1428, comprising a plated through holein substrate 1430. Substrate 1430 may be an interposer, contactor, probecard, or any other suitable electronic component substrate, although aconfiguration suitable for an interposer is shown. The paired contactson each contact pad may be for redundancy, for greater current carryingcapacity, and or for increased mechanical capacity, i.e., increasedstrength or stiffness. In the alternative, one contact 1401, or morethan two contacts 1401, may be provided on each contact pad 1414. Theplan shape of contacts 1401 is shown in FIG. 14A. The curved,semicircular shape of each contact 1401 stays within the periphery ofcontact pad 1414, such as may be desirable, for example, when a smallfootprint is required. Adequate z-extension is provided by a relativelysteep slope, as evident in the edge view shown in FIG. 14B. Horizontalalignment of tips 1406 and the relative z-extension of contacts 1401 arealso shown in the edge view.

In comparison, opposing pairs 1500 of curved contacts 1501 having a moremoderate slope but greater footprint are shown in FIGS. 15A-B, mountedon a substrate 1530 similar to substrate 1430, with annular pads 1514connected by via 1528. The relatively large footprint and longer beamlength are shown in plan view in FIG. 15A. Also visible in FIG. 15A isthe relatively close positioning of each tip 1506 to its correspondingbase 1508, which advantageously reduces delaminating moments on base1508. The more moderate slope provided by the longer beam length isshown in the edge view of FIG. 15B. The greater beam length and moremoderate slope of contact 1501 provides a lower spring rate and greaterworking length, as compared to spring contact 1401. The foregoingexamples are intended only to illustrate general design principlesapplicable to contoured spring contacts, and not to provide actualmodels for use in practice. One skilled in the art may design acontoured spring having the desired properties guided by generalprinciples of mechanical and electrical design, but in most cases,economical development of successful designs for specific applicationswill require the use of more rigorous analytical tools such as finiteelement analysis, as well as thorough testing of prototypes.

In an alternative embodiment, the working range of a system ofmicroelectronic spring contacts may be increased by arranging a pair ofcontacts in series. FIG. 16A shows a plan view of an exemplary contouredspring contact 1600, having a pad-like tip 1606 for mating with thewiping contact tip of another spring contact. A cross-sectional,exploded view of a contact 1600 in series with a contact 1650 having awiping contact is shown in FIG. 16B. Spring contact 1600 is shown with aserpentine beam 1610 and a stiffening rib 1602, but these features areincidental to the function of pad-like tip 1606. Pad-like tip 1606 mayhave a contact surface that is convex, concave, or substantially flat(as shown), and is preferably configured to make electrical contact witha corresponding spring contact having a wiping tip. Hence, pad-like tip1606 preferably has a surface finish conductive to making an electricalconnection, such as a gold layer. Spring contact 1600 may have astiffness (spring constant) somewhat higher than, somewhat lower than,or about the same as, the corresponding contact 1650. Certain advantagesmay accrue from providing a series of contacts 1600, 1650 withdistinctly different spring rates, thereby creating a distinctive stepin contact force after one of the contacts is fully deflected. Forexample, supposing that resilient contact 1600 in FIG. 16B is stifferthan the corresponding resilient contact 1650, as substrate 1630 iscompressed towards substrate 1652, contact 1650 will be deflected firstwhile contact 1600 is substantially undeflected, until the pad-like tip1606 contacts the stop structure 1616. Upon further compression, onlythe second contact 1600 will deflect, and its distinctly higher springrate provides a signal that that contact 1650 is fully deflected. Itshould be apparent that the working range of a series of contacts asshown in FIG. 16B, with proper design, will be the sum of the workingranges of each contact in the series.

Test Head Assemblies

FIG. 17 shows an embodiment of a test head assembly 1700 comprising aprobe card 1702, an interposer 1704 and a contactor 1706. Assembly 1700is similar to, and may be compared to, the probe card assembly shown inFIG. 5 of U.S. Pat. No. 5,974,662 (Eldridge, et al.), which isincorporated herein by reference. However, there are severaldistinguishing differences between the two assemblies, which are madeevident by the description that follows. Assembly 1700 is suitable formaking temporary interconnections to a semiconductor wafer 1708. In thisexploded, cross-sectional view, certain elements of certain componentsare shown exaggerated, for illustrative clarity. However, the alignmentof the various components is properly indicated by the verticalalignment lines in the figure. It should be noted that themicroelectronic spring contacts 1714 and 1716 are shown in full, ratherthan in section.

The probe card 1702 is generally a conventional circuit board substratehaving a plurality (six of many shown) of contact areas 1710 disposed ona surface thereof. Although terminals 1710 are shown as raised pads, itshould be apparent that the terminals may be provided in a variety ofother configurations, including as pads that are flush with the surfaceof the card, or as recessed terminals. Additional components (not shown)may be mounted to the probe card, such as active and passive electroniccomponents, connectors, and the like. The terminals 1710 on the circuitboard may be arranged at a relatively fine pitch, such as about 130microns (about 5 mil). The position and arrangement of terminals 1710 ispreferably related to, but not necessarily identical to, thecorresponding position and arrangement of the terminals on the substrateto be tested. For some applications, terminals 1710 may be arranged atcoarser pitches, such as about 250-2500 microns (about 10-100 mil).However, coarser pitches will likely require the use of a spacetransformer. The probe card 1702 may be suitably circular, having adiameter depending on the application, typically on the order of about30 cm (about 12 inches), or any other desired shape.

The interposer 1704 includes a substrate 1712, which may be comprised ofa ceramic, polymer, or other insulating material, as known in the art.As described above, a plurality (six of many shown) of contouredmicroelectronic spring contacts 1714 are mounted at their bases to andextend from a surface of the substrate 1712, and a correspondingplurality of contoured microelectronic spring contacts 1716 are mountedat their bases to and extend from an opposite surface of the substrate1712. The microelectronic spring contacts 1714 and 1716 are preferably aspecies of integrally formed contact, preferably a contouredmicroelectronic spring contact such as disclosed herein. Any of theaforementioned spring shapes, and various other shapes are suitable forthe contoured microelectronic spring contacts 1714 and 1716. Springcontacts 1714 may be shaped the same as spring contacts 1712, as shownin FIG. 17, or differently from spring contacts 1712. Typically, thetips (distal ends) of both the lower plurality 1714 and of the upperplurality 1716 of contoured spring contacts 1714 and 1716 are disposedat a pitch which matches that of the terminals 1710 of the probe card1702.

The microelectronic spring contacts 1714 and 1716 are illustrated withexaggerated scale, for illustrative clarity. Typically, themicroelectronic spring contacts 1714 and 1716 would extend to an overallheight of about 500-2500 microns (about 20-100 mils) from respectivebottom and top surfaces of the interposer substrate 1712. Generally, theheight of the microelectronic spring contacts is dictated by the amountof compliance desired, which will, in turn, be determined by theplanarity of the test substrate (e.g., wafer 1708), probe card 1702, andcontactor 1706, and the precision with which the position of the testhead assembly may be controlled.

The contactor 1706 comprises a substrate 1718, such as a multi-layerceramic substrate having a first plurality of contact areas or pads 1720disposed on a surface thereof, corresponding to the plurality of springcontacts 1716 on interposer 1704; and a second plurality of contactareas or pads 1722 disposed on the opposite surface thereof, connectedto the first plurality of contact areas. In the embodiment shown, thelower plurality of contact pads 1720 is disposed at the same pitch asthe tips of the microelectronic spring contacts 1716 (e.g., 130 micronsor 5 mils), and the upper plurality of contact pads 1722 is disposed atthe same pitch as the lower plurality of contact pads 1720. Inalternative embodiments, the lower plurality of contact pads may bedisposed at a coarser pitch than the upper plurality of contact pads, inother words, contactor 1706 may be configured as a space transformer.Contact pads 1720, 1722 may be relatively flush with the opposingsurface of contactor (as shown), or may be configured to protrude adistance from the contactor surfaces. In the alternative, resilientinterconnection elements, including but not limited to contouredmicroelectronic spring contacts according to the present invention, orcomposite spring contacts, may be substituted for either or bothpluralities of spring contacts 1716, 1714. For example, contoured springcontacts 1726 may be provided on the contacts pads 1722, to make contactwith contact pads or recessed terminals (not shown) on the wafer. In yetanother embodiment, spring contacts with pad-like tips, such as springcontact 1600 shown in the foregoing FIGS. 16A-B, may be mounted tocontactor 1706 for making contact with spring contacts 1726 on wafer1708. One skilled in the art may devise other suitable combinations ofinterconnection elements, without departing from the scope of theinvention.

A plurality (six of many shown) of resilient microelectronic springcontacts 1726 may be mounted to wafer 1708, each connected to acorresponding terminal for a circuit in the wafer, and each having atleast one contact tip extending from the exposed surface of the wafer.As previously described, these resilient microelectronic spring contacts1726 may be used to accomplish a degree of pitch spreading of theterminals of wafer 1708, so that the tips of spring contacts 1726 arespaced at a coarser pitch (e.g., 250 microns or 10 mil) than theterminals of the wafer to which they are connected, thereby reducing oreliminating the need for further pitch spreading (space transformation)by contactor 1706. Microelectronic spring contacts 1726 are preferably,but not necessarily, a species of contoured microelectronic springcontacts according to the present invention. Spring contacts 1726 areoptionally provided with a stop structure 1728.

Interposer 1704 is disposed over the exposed surface of the probe card1702, and the contactor 1706 is disposed over interposer 1704, as shownin FIG. 7, so that the microelectronic spring contacts 1714 make areliable pressure contact with the contact terminals 1710 of the probecard 1702, and so that the microelectronic spring contacts 1716 ofinterposer 1704 make a reliable pressure contact with the contact pads1720 of the contactor 1706. Any suitable fixture 1750 for supportingthese components and for ensuring such reliable pressure contacts may beemployed, an exemplary one of which is further described below.

The test head assembly 1700 may comprise a fixture 1750 having thefollowing components for holding and aligning the interposer 1706 andthe contactor 1706 onto the probe card 1702: a rear mounting plate 1730;an actuator mounting plate 1732; and a front mounting plate 1734. Eachof the mounting plates may be made of a rigid material such as stainlesssteel. In addition, the assembly 1700 may comprise a plurality (two ofmany shown, three is preferred) of differential adjusting mechanismsincluding an outer differential screw element 1736 and an innerdifferential screw element 1738; a mounting ring 1740 which ispreferably made of a resilient material such as phosphor bronze andwhich has a pattern of resilient tabs (not shown) extending therefrom; aplurality (two of many shown) of screws 1742 for holding the mountingring 1738 to the front mounting plate 1734 thereby capturing thecontactor 1706; optionally, a spacer ring 1744 disposed between themounting ring 1740 and the contactor 1706 to accommodate manufacturingtolerances; and a plurality of pivot spheres 1746, each disposed on anactuating end of one of the differential adjusting mechanisms (e.g., onan end of each inner differential screw element 1738).

The rear mounting plate 1730 is a metal plate or ring disposed on thesurface of the probe card 1702 opposite to the surface on which theinterposer 1704 is mounted. A plurality of holes 1748 extend through therear mounting plate, each for accommodating one of the adjustingmechanisms.

The actuator mounting plate 1732 may be a metal plate or ring disposedon a surface of the rear mounting plate 1730 opposite to probe card1702. A plurality of mounting holes 1750 extend through the actuatormounting plate, each for mounting one of the adjusting mechanisms. Inuse, the actuator mounting plate 1732 may be mounted to the rearmounting plate 1730 in any suitable manner, such as with a plurality ofthreaded fasteners, for example, a plurality of machine screws likescrew 1756.

The front mounting plate 1734 may be a rigid, preferably metal ring.Front mounting plate 1734 may be mounted to the rear mounting plate 1730in any suitable manner, such as with a plurality of threaded fasteners,for example, a plurality of machine screws like screw 1755 extendingthrough corresponding through holes in probe card 1702, therebycapturing the probe card 1702 securely between the front mounting plate1734 and rear mounting plate 1730.

The front mounting plate 1734 may be provided with a mounting surfacedisposed against a surface of probe card 1702, and a large centralopening defined by an inner edge 1752, revealing the plurality ofcontact terminals 1710 of the probe card 1702 to spring contacts 1714,as shown. Front mounting plate 1734 has an inset mounting surface 1762,having a peripheral bezel 1766 to accommodate flange 1764 of contactor1706. Mounting ring 1740 rests against flange 1764 of contactor 1706,and is fastened to the front mounting plate 1734 by a plurality offasteners, as exemplified by machine screw 1742 which may be screwedinto threaded hole 1754. Spacer ring 1744 is optionally placed betweenmounting ring 1740 and front mounting ring 1734, for fine adjustment ofthe gap between contactor 1706 and probe card 1702. A plurality ofthrough holes 1758 (one of many shown) are provided in front mountingplate 1734, each to provide access for one of the differential adjustingmechanisms to bear against contactor 1706 adjacent to inset mountingsurface 1762. A corresponding plurality of through holes 1760 and 1748are aligned through the probe card 1702 and the rear mounting plate,respectively, each to permit passage of one of the adjusting mechanismswhich are mounted to the rear mounting plate 1732.

The pivot spheres 1746 are loosely disposed within the aligned throughholes 1748, 1758 and 1760, each disposed between an end of one of theinner differential screw elements 1738 and contactor 1706. Each of theouter differential screw elements 1736 thread into one of the threadedholes 1750 of the actuator mounting plate 1732, and the innerdifferential screw elements 1738 thread into a threaded bore of theouter differential screw elements 1736. Very fine adjustments can bemade in the positions of the individual pivot spheres 1746 using such adifferential adjustment mechanism, as discussed in more detail in theabove-referenced U.S. Pat. No. 5,974,662. Interposer 1704 is preferablyconfigured (by selecting spring contacts with appropriate ranges ofmotion) to ensure that electrical connections are maintained between thecontactor 1706 and the probe card 1702 throughout the contactor's rangeof adjustment. Other details of test head assembly 1700 are the same as,or may readily be adapted from, the aforementioned probe card assemblydisclosed in U.S. Pat. No. 5,974,662.

In an alternative embodiment, a test head assembly is provided with acontactor having a plurality of contoured microelectronic springcontacts, and the interposer is omitted. FIG. 18 shows a test headassembly 1800 according to an embodiment with no interposer. Except forthe configuration of contactor 1806 and the lack of an interposer,assembly 1800 may comprise many of the same elements as assembly 1700,and may be configured similarly. In the embodiment shown in FIG. 18,mounting ring 1840, front mounting plate 1834, probe card 1802, rearmounting plate 1830, actuator plate 1832, the adjustment mechanismcomprised of inner and outer screws 1836 and 1838, and the associatedscrews, through holes, and so forth, comprise a fixture 1850 that isconfigured the same as the corresponding elements fixture 1750 and itscomponents shown in FIG. 17. Wafer 1808, however, is provided withnon-resilient contact pads 1826 instead of resilient contact elements.Contactor 1806 is configured much as if it were an interposer, withinterconnected pluralities (six of many shown) of contouredmicroelectronic spring contacts 1814 and 1816 mounted to its opposingfaces. Flange 1864 is configured differently to permit the contactor tofit both inside bezel 1866 and the opening defined by edge 1858. In thealternative, the openings in the front mounting ring 1834 may beconfigured differently to account for the missing interposer.

Spring contacts 1814 and 1816 are shown to be the same type as shown oninterposer 1704 of assembly 1700, but it should be understood that thisneed not be the case. Any suitable shape may be used, and it may bedesirable to configure one or both pluralities of contacts 1816, 1814 toprovide a relatively large elastic range of motion. Either or both ofwafer 1808 and probe card 1802 may be provided with resilientfree-standing spring contacts having a contact tip designed to mate witha corresponding one of spring contacts 1814 and 1816. For example, toprovide for greater adjustability between probe card 1802 and contactor1806, it may be particularly advantageous to provide each contact 1810of probe card 1802 with a spring contact having a pad-like tip, such asshown in FIGS. 16A and 16B. In this way, contactor 1806 can be providedwith adjustability through two sets of linked spring contacts, therebyachieving a range of adjustability comparable to an interposer. Similarresilient contacts may also be provided on wafer 1808.

Test head assemblies according to the present invention will perform aswell as or better than prior art assemblies using composite springcontacts, but at a potentially lower cost. Such assemblies can providesubstantial advantages over prior art test apparatus, including a highdensity of contacts that may be as high as the contact density on thedevices under test, and suitability for performing wafer-level burn-inand testing, as described in more detail in U.S. Pat. No. 6,064,213,which is incorporated herein by reference. Other features of probe cardor test head assemblies described in the foregoing references mayreadily be incorporated into an assembly according to the presentinvention. Such variations in the present assembly will be apparent uponinspection of the incorporated references.

Having thus described a preferred embodiment of the substrates withpluralities of contoured microelectronic spring contacts, it should beapparent to those skilled in the art that certain advantages of thewithin system have been achieved. It should also be appreciated thatvarious modifications, adaptations, and alternative embodiments thereofmay be made within the scope and spirit of the present invention. Forexample, semiconductor dies and wafers, LGA sockets, and test headassemblies have been illustrated, but it should be apparent that theinventive concepts described above would be equally applicable tovarious other types of substrates and electronic components. Theinvention is further defined by the following claims.

1. An electronic component, comprising: at least one face; a pluralityof microelectronic spring contacts mounted to said at least one face,each of said plurality of microelectronic spring contacts comprising abase mounted to said at least one face, a contoured beam integral withsaid base and extending from a side of said base away from said at leastone face, and a free end of said beam opposite to said base, whereinsaid beam has an unsupported span between said free end and said base,and wherein each of said microelectronic spring contacts comprises anintegral layer of resilient material.
 2. The electronic component ofclaim 1, wherein said electronic component further comprises a die cutfrom a semiconductor wafer, said die comprising an integrated circuithaving a plurality of terminals on said at least one face thereof,wherein selected ones of said plurality of microelectronic springcontacts are connected to selected ones of said plurality of terminals.3. The electronic component of claim 1, wherein said electroniccomponent further comprises a semiconductor wafer, said wafer comprisinga plurality of integrated circuits having a plurality of terminals onsaid at least one face thereof, wherein selected ones of said pluralityof microelectronic spring contacts are connected to selected ones ofsaid plurality of terminals.
 4. The electronic component of claim 1,wherein said electronic component further comprises an integratedcircuit socket, said socket comprising a back surface opposing said atleast one face, said back surface having a plurality of terminals,wherein selected ones of said plurality of microelectronic springs areconnected to selected ones of said terminals.
 5. The electroniccomponent of claim 1, wherein said electronic component furthercomprises an interposer, said interposer comprising a substrate having asecond surface opposing said at least one face; and a second pluralityof microelectronic spring contacts mounted to said second surface, eachof said second plurality of microelectronic spring contacts comprising abase mounted to said at least one face, a contoured essentiallysheet-like beam integral with said base and extending from a side ofsaid base away from said at least one face, and free end of said beamopposite to said base, wherein said beam has an unsupported span betweensaid tip and said base, and wherein each of said microelectronic springcontacts comprises an integral layer of resilient material; wherein onesof said second plurality of microelectronic spring contacts areconnected to ones of said plurality of microelectronic spring contactson said at least one face.
 6. The electronic component of claim 5,wherein said electronic component further comprises a test headassembly, said assembly comprising: a fixture, said interposer supportedby said fixture; and a contactor coupled to said interposer.
 7. Theelectronic component of claim 1, wherein said electronic componentfurther comprises a test head assembly, said assembly comprising: afixture; and a contactor supported by said fixture, said contactorcomprising said at least one face.
 8. The electronic component of claim1, wherein said beam, viewed in a direction normal to said substratesurface, is tapered so as to have a generally triangular shape.
 9. Theelectronic component of claim 1, wherein each of said microelectronicspring contacts is formed by depositing the integral layer of resilientmaterial on a sacrificial layer using a method selected fromelectroplating, electroless plating, sputtering, chemical vapordeposition, or physical vapor deposition.
 10. The electronic componentof claim 1, wherein each of said microelectronic spring contacts furthercomprises a contact tip adjacent to said free end of said beam.
 11. Theelectronic component of claim 1, wherein said beam, viewed in adirection normal to said substrate surface, has a generally rectangularshape.
 12. The electronic component of claim 1, wherein said beam,viewed in a direction normal to said substrate surface, has an offsetwith respect to a central axis.
 13. The electronic component of claim 1,wherein said beam, in a lengthwise sectional view, has a linear shape.14. The electronic component of claim 1, wherein said beam, in alengthwise sectional view, has an arcuate shape.
 15. The electroniccomponent of claim 1, wherein said beam, in a lengthwise sectional view,has a corrugated shape.
 16. The electronic component of claim 1, whereinsaid beam, in a lengthwise sectional view, has a stepped portion nearthe base.
 17. The electronic component of claim 1, wherein said beam, ina cross sectional view, is generally V-shaped.
 18. The electroniccomponent of claim 1, wherein said beam, in a cross sectional view, isgenerally U-shaped.
 19. The electronic component of claim 1, whereinsaid spring includes a lengthwise rib extending over at least a portionof the beam.
 20. The electronic component of claim 19, wherein saidbeam, in a lengthwise sectional view, has a stepped portion adjacent thebase, and wherein said lengthwise rib extends to said stepped portion.21. The electronic component of claim 19, wherein said lengthwise ribextends to said base.
 22. The electronic component of claim 19, whereinsaid lengthwise rib extends into said base.
 23. The electronic componentof claim 19, wherein said lengthwise rib comprises a lengthwise channel.24. The electronic component of claim 23, wherein said lengthwisechannel has a regular geometric cross-sectional shape.
 25. Theelectronic component of claim 24, wherein said regular geometriccross-sectional shape is a shape selected from the group consisting ofpart-rectangular, part-trapezoidal, part-triangular and part-roundshapes.
 26. The electronic component of claim 19, wherein thecross-sectional dimensions of said lengthwise rib are similar over thelength thereof.
 27. The electronic component of claim 19, wherein across-sectional dimension of said lengthwise rib differs over the lengththereof.
 28. A method for testing an integrated circuit comprising:providing a die having a substantially planar surface that has aplurality of microelectronic spring contacts formed on the surface,where each of the microelectronic spring contacts comprises a basemounted to the surface, a beam integral with the base and extending froma side of the base away from the surface, and free end of the beamopposite to the base, wherein the beam has an unsupported span betweenthe free end and the base, and is capable of at least some flexure alongan axis perpendicular to the wafer surface, and wherein each of saidmicroelectronic spring contacts comprises an integral layer of resilientmaterial; contacting an integrated circuit with the spring contacts ofthe die; and testing an integrated circuit of the die during saidcontacting step after backend processing of the die.
 29. A method fortesting a wafer including a plurality of integrated circuits comprising:providing a wafer having a substantially planar surface that has aplurality of microelectronic spring contacts formed on the surface,where each of the microelectronic spring contacts comprises a basemounted to the surface, a beam integral with the base and extending froma side of the base away from the surface, and free end of the beamopposite to the base, wherein the beam has an unsupported span betweenthe free end and the base, and is capable of at least some flexure alongan axis perpendicular to the wafer surface, and wherein each of saidmicroelectronic spring contacts comprises an integral layer of resilientmaterial; contacting a wafer having a plurality of integrated circuitsformed thereon with the spring contacts of the substrate; and testing aplurality of integrated circuits of the wafer during said contactingstep prior to backend processing of said wafer. 30-33. (canceled)
 34. Atest head assembly comprising: a probe card comprising a plurality offirst contact areas; a contactor comprising a plurality of secondcontact areas; and an interposer comprising a plurality of first springcontact structures each contacting one of said first contact areas, anda plurality of second spring contact structures each contacting one ofsaid second contact areas, wherein ones of said first spring contactstructures are electrically connected through said interposer to ones ofsaid second spring contact structures, wherein ones of said first springcontact structures or ones of said second spring contact structurescomprise electrically connected pairs of contacts extending away from asurface of said interposer.
 35. The test head assembly of claim 34,wherein ones of both said first spring contact structures and saidsecond spring contact structures comprise electrically connected pairsof contacts extending away from a surface of said interposer.
 36. Thetest head assembly of claim 34, wherein each of said pairs of contactscomprise opposing curved beams.
 37. The test head assembly of claim 34,wherein each of said pairs of contacts comprise mirror image beams. 38.A test head assembly comprising: a probe card comprising a plurality offirst contact areas; a contactor comprising a plurality of devicecontacts for contacting an electronic device to be tested; and a firstplurality of pairs of spring contacts, each pair of spring contactselectrically connecting one of said contact areas with one of saiddevice contacts.
 39. The test head assembly of claim 38, wherein each ofsaid device contacts comprises a pair of beams.
 40. The test headassembly of claim 38, wherein each of said pairs of spring contactscomprise opposing curved beams.
 41. The test head assembly of claim 38,wherein each of said pairs of spring contacts comprise mirror imagebeams.